Office chairs are known, generally consisting of a support base provided with wheels and a rotatable column of variable height, the upper end of which is inserted into a box support internally housing the adjustment mechanisms for the seating portion and back rest.
These structures are subjected to intensive use and consequently have to be able to resist the tests required by international regulations of this sector.
One of the points most subjected to structural stresses is the connection between the structure and the rotatable column, which generally consists of a traditional gas spring enabling the seating portion to be height adjusted. Generally the connection between the column and the structure is obtained by a male conical part provided in the head of the column and insertion-fitted into a corresponding female conical part obtained in the structure.
A first known type of box support is obtained by die-casting aluminum.
However, this structure has the drawback of a high cost due to the materials used, to the die-casting operations, and to the metal structure finishing operations and the grinding of tolerance holes.
Moreover, all the holes in which pins rotate require the use of costly self-lubricating sockets to prevent seizure and jamming of movements.
Chair structures have also been obtained by pressing sheet metal parts followed by welding the steel sockets.
This solution has however the drawback of high cost due to welding and painting operations.
Moreover, with this solution, self-lubricating sockets again have to be used, and the pieces obtained are considerably limited in terms of shape.
Products have also been proposed with an integral plastic structure or with steel cones fitted together or over-molded, but the structural characteristics are insufficient for intensive product use. Moreover the cost of this possible conical component, usually obtained by lathe turning or from a tube, is high.
The object of the invention is to eliminate these drawbacks by providing a structure for office chairs which is simple, comfortable and highly reliable.